It might be Iruka - sensei. Iruka was one of the first people to recognize Naruto for who he was and give him a sense of belonging. If Iruka were to die, Naruto would remember all those early days of support and kindness. His death would break Naruto's heart as it would be like losing a part of his family, the family that accepted him when no one else did.
Another possibility is Jiraiya. Jiraiya was Naruto's teacher and a father - figure to him. If Jiraiya were killed, Naruto would be inconsolable. He would cry for the loss of his mentor, the one who taught him so much about being a ninja and about life in general. His death would also make Naruto question his own strength and whether he's ready to face the challenges ahead without Jiraiya's guidance.
One possible plot could be that Naruto witnesses the death of a fellow ninja from his village during a battle. Maybe it's someone he has trained with or has a friendly rivalry. This would cause him to cry as he feels a deep sense of loss for his comrade and also blames himself for not being able to protect them.
It could be a random civilian. This would show Naruto the impact of the ninja world's violence on ordinary people, making him more determined to protect the innocent.
This event can be a huge turning point for Naruto. It might make him more determined to protect others. He could become more serious about his training and his goal of bringing peace to the ninja world. Seeing the death might also make him more empathetic towards those who have lost loved ones.
It might be an old enemy of Naruto who has come back for revenge. For example, someone from the Akatsuki who wasn't completely defeated before. They could target Naruto again and put him in a life - threatening situation, which makes Kurama cry.
The aftermath could be Minato's quest for revenge if Naruto's death was caused by someone. He would use his skills and knowledge to track down those responsible. Or, he could be plunged into a deep depression. He might isolate himself from the other spirits or entities in the afterlife. His whole existence could become centered around his grief and his memories of Naruto.
It could be a new character, perhaps someone from a far - off land who has a grudge against Naruto's future self for some reason. This character might be extremely powerful and has plans to destroy everything Naruto holds dear. When Naruto sees this future, he has to find a way to stop this new threat before it even begins to form.
Well, Naruto might be really confused at first. He's from his own world and an AMV (Anime Music Video) fanfiction is a very modern and fan - created concept. He could be intrigued by the different interpretations of his story or his friends' stories in the fanfiction.
Minato would likely be devastated. He sacrificed his life for Naruto, hoping for a great future for his son. Seeing Naruto die would shatter his hopes and dreams. He might first be in denial, unable to believe what he's seeing. Then, his grief could turn to anger, either at the situation or at those he believes are responsible. It's a tragic scenario that would change Minato's afterlife perception and his sense of purpose, which was always tied to Naruto's well - being.
Obviously, Naruto himself is the most affected as he has to deal with the knowledge of the future. But his friends like Sasuke, Sakura, and Kakashi would also be deeply affected. If Naruto saw a future where Sasuke was in trouble, he would do everything to change it, which would impact Sasuke's life. Sakura, being Naruto's teammate and also caring about Sasuke, would be involved in any plan Naruto made. And Kakashi, as their sensei, would be there to guide and support them through the changes Naruto tries to make based on his future vision.
It could be a dark ninja who also has the ability to manipulate spirits. He might use this power to create chaos in the ninja world and Naruto has to stop him while also dealing with the spirits he sees.